A semiconductor device such as an IC (integrated circuit) generally has electronic circuit elements such as transistors, diodes and resistors fabricated integrally on a single body of semiconductor material. The various circuit elements are connected trough conductive connectors to form a complete circuit which can contain millions of individual circuit elements. Advances in semiconductor materials and processing techniques have resulted in reducing the overall size of the IC circuit elements while increasing their number on a single body. Additional miniaturization is highly desirable for improved IC performance and cost reduction. Interconnects provide the electrical connections between the various electronic elements of an IC and they form the connections between these elements and the device's external contact elements, such as pins, for connecting the IC to other circuits. Typically, horizontal interconnects form horizontal connections between electronic circuit elements while vertical interconnects form vertical connections between the electronic circuit elements, resulting in layered connections. Horizontal interconnects are also referred to as interconnect lines, wires or traces, while vertical interconnects are also known as interconnect lines, vias, plugs or studs.
A variety of conventional techniques are employed for fabricating IC interconnects of semiconductor devices. For example a horizontal interconnect can be formed by etching a channel or trench in an insulating layer of a semiconductor device, using a variety of wet or dry etching techniques. The channel is then filled with a highly conductive material, such as for example copper, resulting in a horizontal interconnect. A layer having a horizontal interconnect line is typically known as a metal layer, while a layer that is disposed between two horizontal metal layers is commonly referred to as an intra metal layer or insulating layer. A vertical interconnect can similarly be formed by etching a hole through an insulating layer of a semiconductor device and then filling the hole with a highly conductive material resulting in a vertical interconnect line. It is a common practice in semiconductor wafer fabrication to form integrated circuits wherein a horizontal interconnect is formed on the exposed top surface of one or more vias or vertical interconnects. Similarly it is a conventional technique to from one or more vias or vertical interconnects on the exposed top surface of a horizontal interconnect. Generally, the layer in which the interconnect is formed remains, at least partly, in the finished semiconductor device. However, it is also known to remove the layer wherein the interconnect has been formed, and then replacing this layer with another material as shown in U.S. Pat. No. 6,153,521 (2000, Cheung et al.). The Cheung et al. patent teaches forming a horizontal interconnect line in a trench that is formed in a layer of sacrificial material. Following fabrication of the interconnect line in the trench, the sacrificial layer is removed thereby resulting in a free standing interconnect line. A conformal layer of conventional insulating material is then deposited on the interconnect line. The conformal layer is subjected to CMP (chemical mechanical polishing) to expose and define the interconnect line. As shown in the Cheung et al. patent, the line can be formed in contact with via plugs in an underlying insulating layer. Alternatively, the line can be formed by utilizing a sacrificial trench overlaying via holes, and then simultaneously filling the via holes and the trench with a metal. This technique of simultaneously filling a trench and underlying via hole is commonly known as dual damascene. The term “single damascene” is typically employed for techniques wherein the interconnect line and the underlying via are formed separately.
Lopatin et al. (U.S. Pat. No. 6,259,160, 2001) teach forming a via in a hole that is lined with a barrier layer to prevent metal diffusion into the insulating layer within which the via is formed. Subsequently, a metal interconnect line is formed in a trench overlaying the via, wherein the trench is formed in the sacrificial layer. The sacrificial layer is then removed, thus forming a free standing interconnect line which is subsequently encapsulated in a barrier layer. As a result, the Lopatin et al. via and interconnect line are encapsulated in a metal diffusion barrier layer. An insulating material is deposited on the interconnect line containing structure. A via hole can be prepared in the insulating layer such that the hole contacts the encapsulated interconnect line. One of the embodiments of U.S. Pat. No. 6,376,374 (Stevens, 2002) teaches depositing a barrier layer on a substrate and, if necessary, depositing a seed layer on the barrier layer. A metal interconnect line is formed
in a trench of a first sacrificial layer that is deposited on the barrier layer or the barrier/seed layer. The first sacrificial layer is removed resulting in a free standing interconnect line. A second sacrificial layer is prepared on the interconnect line and on the barrier or barrier/seed layer. The second sacrificial layer is developed to form a via hole on the interconnect line, such that the via hole exposes a portion of the metal line. The via hole is then filled with metal to from a via plug, after which the second sacrificial layer is removed, thus resulting in a free standing structure comprising a via that is fabricated on a metal line. Thereafter, portions of the barrier or barrier/seed layer extending beyond the interconnect are removed. The top and sides of the resulting interconnect line and via structure are then partly or completed oxidized. Non-oxidized portions of the surface of the structure are subsequently coated with a barrier layer to impede metal migration from the line and/or via. A layer of insulating material is deposited on the oxidized and coated structure and on exposed segments of the substrate. The upper surface of the insulating layer is then treated to expose the top surface of the via that is fabricated on the interconnect line.
A need exists for improved fabricating techniques of structures, such as those exemplified in the above referenced patents, to improve IC device manufacturing yield, device reliability and manufacturing cost.
Copper, due to its low electrical resistance, is a preferred metal for IC interconnects. However, it is well known that copper components, such as deposits that are formed in a typical IC dielectric layer, are difficult to define when using CMP. For example, Cu surfaces tend to dish, i.e. forming a slightly hollow top surface, during CMP. It is therefore desirable to improve IC fabricating techniques in order to mitigate, or eliminate where possible, IC fabricating difficulties or inefficiencies resulting from the use of copper.
Furthermore, as a consequence of the well known need for increasing the circuit density, it is desirable to develop fabrication technologies that utilize etching and deposition openings that have a small diameter and a high aspect ratio.